Refrigerating apparatus with defrosting means



A. J. KUHN April 17, 1962 REFRIGERATING APPARATUS WI'TH DEFROSTING MEANS Filed NOV. 16, 1959 Th Nb 1. m J M r m m s m m Y B 8 3 2 im 6 T United States Patent aware v Filed Nov. 16, 1959, Ser. No. 853,265 1 Claim. (Cl. 62-156) This invention relates to refrigerating apparatus and more particularly to an automatic control arrangement for use in periodically defrosting a refrigerator evaporator.

' It is an object of this invention to provide a defrost control system for a domestic refrigerator wherein a time clock is used for automatically initiating operation of a defrost heater at timed intervals and wherein a defrost limiter switch is used for automatically deenergizing the defrost heater and for 'reestablishing operation of the refrigerant compressor.

Another object of this invention is to provide a control circuit for a refrigerant compressor and a defrost heater wherein a time clock selectively connects either the heater or the compressor to a power source and wherein a thermostat responsive to the evaporator temperature can initiate operation of the compressor even though the time clock operated switch has not reclosed the main circuit to the compressor motor. 7

These and further objects and advantages of the present invention will be apparent from the following description, reference being had to the accompanying drawing wherein a preferred embodiment of the present invention is clearly shown.

In the drawing:

FIGURE 1 diagrammatically shows a refrigerating system of the type embodying the invention.

FIGURE 2 is a schematic circuit diagram showing the controls for the apparatus shown in FIGURE 1.

Referring now to the drawing wherein a preferred embodiment of the invention has been shown, reference numeral 10 designates a sealed motor compressor unit which serves to discharge compressed refrigerant into a condenser 12 from whence the'condensed refrigerant is fed into the evaporator 14 through a pressure reducing device 16. For purposes of illustration a single evaporator located in an insulated food storage compartment 17 has been shown whereas the invention is equally applicable to systems wherein a plurality of evaporators or evaporator sections are used to cool a plurality of different compartments. Copending application Serial No.

575,639, filed April 2, 1956, and now abandoned, shows a refrigerator of the type in which my improved defrost control system could be used to great advantage to reduce the cost of the controls.

The main power lines 26 and 28 serve to supply power to the apparatus and controls by means of the circuit shown in FIGURE 2 of the drawing. The operation of the motor compressor unit 10 is controlled by a time clock 20 through a single-pole, double-throw switch 22 which serves to selectively energize either that portion of the circuit which includes the motor compressor unit 10 or that portion of the circuit which includes the evaporator defrost heater 24.

At given intervals when it is desired to stop the compressor and defrost the evaporator 14, the switch 22 moves from its solid line position, shown in FIGURE 2, to its dotted line position, in which position it closes a circuit to the defrost heater 24. The time clock is preferably designed to open the compressor motor circuit once every twenty-four hours and to close the defrost heater circuit for a given period of time such as thirty minutes. This period must be long enough to provide complete defrosting of the evaporator 14 during the most adverse frost forming conditions.

Since this period of time obviously must be selected to "be greater than the time required for completely defrosting the evaporator under the minimum frost forming conditions, it is desirable to provide some added form of control which will not only cause the defrost heater to be deenergized immediately upon the completion of defrosting but which will also initiate operation of the compressor so as to produce refrigeration before the food stored inthe refrigerator becomes too warm. It the past rather complex and expensive controls have been used for this whereas in the system disclosed herein, a single-pole, double-throw switch 32 is used which responds to the temperature of the evaporator and which serves the dual function of preventing excessive evaporator temperatures and intitating operation of the compressor motor immediately upon completion of the defrosting of the evaporator 14 even through the clock operated switch 22 has not reclosed the circuit to the compressor. In order to simplify the disclosure the switch 32 has been shown schematically and is intended to represent a conventional snap acting bimetallic defrost limiter switch which serves to open the circuit through the upper switch contact 34 and close the circuit through the lower contact 36 whenever the temperature of the evaporator 14 exceeds 50 F. and to reclose the circuit through the contact 34 when the evaporator temperature drops to 20 F.

A conventional cycling control thermostat 38 responsive to refrigeration requirements is arranged in the compressor circuit, as shown, and serves to cycle the compressor in accordance with conventional practice during the normal operation of the refrigerating system. For purposes of illustration the thermostat 38 has been shown arranged to respond to changes in the temperature of the evaporator 14 whereas it could respond to changes in the temperature ofthe air in the food compartment for example. It will be noted that the thermostat 32 can only energize the compressor when the clock operated switch 22 occupies the dotted line position and when the thermostat 38 is closed. When the switch 22 occupies its full line position, the thermostat 38 is the sole means for controlling the operation of the compressor.

While the embodiments of the present invention as herein disclosed, constitute preferred forms, it is to be understood that other forms might be adopted.

What is claimed is as follows:

In a refrigerator, an insulated cabinet having a food storage compartment, a refrigeration system including a compressor and an evaporator for cooling said compartment, heating means for defrosting said evaporator, circuit means including a first single pole double throw switch for selectively connecting either said compressor or said heating means to a source of power, said circuit means including a first branch in which said heater is connected and a second branch in which said compressor is connected, means including a second single pole double throw switch responsive to the temperature of said evaporator and arranged in series with said first switch for interrupting the circuit to said heater and establishing a circuit to said motor compressor unit, and temperature responsive means arranged in series with said compressor for cycling said compressor in response to refrigeration requirements.

References Cited in the file of this patent UNITED STATES PATENTS 2,863,300 Murphy Dec. 9, 1958 FOREIGN PATENTS 807,812 Great Britain 'Jan. 21, 1959 

